Charles W. Bostian

Measurements and models of radio frequency impulsive noise for indoor wireless communications

The authors present the results of average and impulsive noise measurements inside several office buildings and retail stores. The noise measurement system operated at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40-MHz, 3-dB RF bandwidth. Omnidirectional and directional antennas were used to investigate the characteristics and sources of RF noise in indoor channels. Statistical analyses of the measurements are presented in the form of peak amplitude probability distributions, pulse duration distributions, and interarrival time distributions. Simple first-order mathematical models for these statistical characterizations are also presented. These analyses indicate that photocopiers, printers (both line printers and cash register receipt printers), elevators, and microwave ovens are significant sources of impulse noise in office and retail environments. >

Analog-to-digital converters

This paper analyzed the internal relationships of the performance parameters of ADCs, showing their frequency dependency and structure dependency. The history and current trends in ADC technologies based on the P and F figures-of-merit were also reviewed. Historically, there was an increase in performance around 1994, with a share rise around 1997, which broke the stagnant performance discussed by Waiden (1999). While the past few years have shown a sharp increase in ADC performance, we have shown that performance and power dissipation depend greatly on the ADC structure and the target applications. With the progression of wideband radio systems like UWB and OFDM comes a growing demand to provide faster sampling rates and higher resolutions with lower power dissipation. With the innovation of advanced communication techniques like multi-input/multi-output and multistandard radios, the demand is growing to provide multichannel programmable data conversion, both of which are pushing the performance of ADCs further in the coming years.

Cognitive Radio and Networking Research at Virginia Tech

More than a dozen Wireless @ Virginia Tech faculty are working to address the broad research agenda of cognitive radio and cognitive networks. Our core research team spans the protocol stack from radio and reconfigurable hardware to communications theory to the networking layer. Our work includes new analysis methods and the development of new software architectures and applications, in addition to work on the core concepts and architectures underlying cognitive radios and cognitive networks. This paper describes these contributions and points towards critical future work that remains to fulfill the promise of cognitive radio. We briefly describe the history of work on cognitive radios and networks at Virginia Tech and then discuss our contributions to the core cognitive processing underlying these systems, focusing on our cognitive engine. We also describe developments that support the cognitive engine and advances in radio technology that provide the flexibility desired in a cognitive radio node. We consider securing and verifying cognitive systems and examine the challenges of expanding the cognitive paradigm up the protocol stack to optimize end-to-end network performance. Lastly, we consider the analysis of cognitive systems using game theory and the application of cognitive techniques to problems in dynamic spectrum sharing and control of multiple-input multiple-output radios.

Cognitive radio testbed: further details and testing of a distributed genetic algorithm based cognitive engine for programmable radios

This paper provides details of a distributed genetic algorithm (GA) based cognitive radio engine model for disaster communications and its implementation in a cognitive radio test bed using programmable radios. Future applications include tactical and covert communications. The cognitive system monitor (CSM) module presented here permits cross layer cognition and adaptation of a programmable radio by classifying the observed channel, matching channel behavior with operational goals, and passing these goals to a wireless system genetic algorithm (WSGA) adaptive controller module to evolve and optimize radio operation. The CSM module algorithm provides for parallel distributed operation and includes a learning classifier and meta-GA functions that work from a knowledge base (which may be distributed) in long term memory to synthesize matched channels and operational goals that are retained in short term memory. Experimental results show that the cognitive engine finds the best tradeoff between a host radios operational parameters in changing wireless conditions, while the baseline adaptive controller only increases or decreases its data rate based on a threshold, often wasting usable bandwidth or excess power when it is not needed due its inability to learn.

Cognitive radio applications to dynamic spectrum allocation: a discussion and an illustrative example

In an effort to improve radio spectrum management and promote a more efficient use of it, regulatory bodies are currently trying to adopt a new spectrum access model. At the same time, cognitive radio technology has received a lot of interest as a possible enabling technology. In this paper, we provide a brief description of the broad impact of cognitive radios in different markets. At Virginia Techs Center for Wireless Telecommunications (CWT), we have designed a biologically inspired cognitive engine with dynamic spectrum access (DSA) as one of its intended applications. An experimental software simulation shows a 20 dB SINR improvement using cognitive techniques in an interference environment over that provided by current IEEE 802.11a service PHY standard

Online modeling of wireless channels with hidden Markov models and channel impulse responses for cognitive radios

A cognitive radio must be able to observe and model the channel in which it operates. As a first step to creating a truly cognitive radio, we have developed a novel technique to model wireless channels by combining a broadband channel sounder with a wireless channel genetic algorithm (WCGA). The WCGA receives a sequence of error symbols simulated from the impulse response to train a hidden Markov model (HMM) with a genetic algorithm. The HMM is a compact representation of the channel that a radio can create online and then use as the input to a cognitive process for intelligent adaptation of the radio.

Implementing adaptive power control as a 30/20-GHz fade countermeasure

Satellite systems in the 30/20-GHz band are very susceptible to outages due to rain-induced fades. In order to reduce the impact of these fades, it has been proposed that the power of a transmitting ground station be adjusted during the fade to compensate for the additional attenuation. Real-time frequency scaling of attenuation from the downlink to the uplink shows promise for estimating the uplink attenuation for uplink power control (ULPC). A scaling-type ULPC algorithm using 20-GHz attenuation scaled to 30 GHz is presented. The limitations of such an algorithm and the effects of scintillation on ULPC are explored. The algorithm is tested using OLYMPUS fade data measured on the 14/spl deg/ elevation OLYMPUS to Blacksburg, VA path. An ULPC scheme employing a beacon at the uplink is also presented. It offers better performance than scaled downlink attenuation ULPC.

Cognitive Radio Platform Development for Interoperability

In this paper, we present a general method to reconfigure a software defined radio (SDR) using a set of intelligent algorithms called a cognitive engine (CE) to create a cognitive radio (CR) that provides a user with a required quality of service (QoS). The proposed architecture relies on the CE to generate an XML document that describes the SDR behavior. An application programming interface (API) translates the XML document to the platform-specific commands to adjust the SDR. The API structure developed here will find initial applications in public safety and military communications to provide low-cost, multi-band, multi-mode operation for interoperability with SDR technology

A deterministic approach to predicting microwave diffraction by buildings for microcellular systems

A propagation prediction method that exploits a building database and considers the three-dimensional profile of the radio path is presented. Models and algorithms are provided that allow the application of Fresnel-Kirchhoff diffraction theory to arbitrarily oriented buildings of simple shapes. Building location information used by the diffraction models is in a form compatible with a geographic information system (GIS) database. Diffraction screens are constructed at all building edges, for both horizontal and vertical orientations, in order to consider all possible diffractions, and to compute field contributions that are often ignored. Multiple buildings and edges of the same building that introduce multiple successive diffractions are considered with a rigorous, recursive application of the diffraction theory that requires sampling the field distribution in each aperture. Robust and computationally efficient numerical methods are applied to solve the diffraction integrals. >

The resurgence of push-to-talk technologies

Push-to-talk (PTT) technologies date back to the advent of the telegraph and more recently have been the domain of traditional land mobile radio (LMR) networks. The past few years have brought about a resurgence in PTT as a service offered by commercial providers, driven first by private subscribers and, increasingly, by organizations such as law enforcement agencies that traditionally rely on LMRs. This technology, today one of the growth areas in the communications industry, has received little attention in the scientific literature. In this article, we discuss some of the emerging technologies (voice over IP, CDMA used in 2.5G/3G systems) that relate to todays PTT service. We also discuss the market and financial implications of commercial PTT on current LMR deployments.